Image processing method, image processor, and image display system

ABSTRACT

An image processing method, which performs color correction on a superimposed image obtained by superimposing a first image formed by a first image forming unit and a second image formed by a second image forming unit, includes controlling the dimming of the first image forming unit and the second image forming unit on the basis of dimming rates set in the first image forming unit and the second image forming unit in response to a given designated dimming rate, and performing a color correction process on image signals corresponding to the first image forming unit and the second image forming unit using a color correction value corresponding to the dimming rates of the first image forming unit and the second image forming unit.

This is a Continuation of application Ser. No. 13/530,908 filed Jun. 22,2012. The disclosure of the prior application[s] is hereby incorporatedby reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to an image processing method, an imageprocessor, and an image display system.

2. Related Art

As a technique for improving resolution and brightness of a projector, astack display technique in which images projected from a plurality ofprojectors are stacked to display one image is known. Similarly to animage displayed by a single projector, a stack image has luminanceunevenness or color unevenness. In general, correction of luminanceunevenness or color unevenness is performed on the entire screen basedon the darkest portion within the screen when white display is performed(that is, when an image of white which is the brightest image from amongimages to be displayed by a projector is displayed). As a result ofcorrection, brightness of white is degraded.

FIGS. 28A and 28B are explanatory views of a general unevennesscorrection principle. FIG. 28A shows an example of a change in luminancein a horizontal direction of a screen as the state of luminanceunevenness when white display is performed for simplification ofdescription. FIG. 28B schematically shows the change in luminance ofFIG. 28A in a stepwise manner. In FIGS. 28A and 28B, the horizontal axisrepresents the pixel position of the screen and the vertical axisrepresents luminance (in a broad sense, intensity).

The change in luminance shown in FIG. 28A when white display isperformed is viewed as image unevenness. In this case, in general,correction is performed such that the luminance of each position has theminimum value Ymin when the minimum value Ymin of luminance shown inFIGS. 28A and 28B is set as a target value for unevenness correction.This is because, when white display is performed, the whole portion maynot be increased in luminance, such that, if the luminance of a portionother than the darkest portion is set as a target value for unevennesscorrection, the luminance of the darkest portion may not conform to thetarget value. For this reason, unevenness correction for improvingdisplay quality is performed in a direction in which brightness of whiteis degraded.

A projector has an inherent color characteristic, and if no correctionis performed, the display characteristic may be considerably shiftedfrom the standard colors, such as sRGB (standard RGB). If correction(color correction) is performed to match the colors to the target color,this causes the degradation of brightness of the projector.

FIG. 29 is an explanatory view of a general color correction principle.FIG. 29 schematically shows the state where a target output luminancecharacteristic to be displayed and an actual characteristic (actualdevice characteristic) of a projector are associated with each otherusing LUT (Look-Up Table) data in which unevenness correction values aretabulated.

For example, in order to realize transmittance T0 when a voltage V0 isapplied, it is necessary to apply a voltage V1 according to the actualcharacteristic inherent in the projector. Accordingly, a search iscarried out for the actual characteristics (input/outputcharacteristics) of the projector measured in advance to create LUT datashown in FIG. 29. In the color correction, the voltage for realizingtransmittance T0 is corrected to a voltage specific to the projectorusing LUT data. When a single liquid crystal panel as an opticalmodulator is provided, LUT data can be set directly by a single search.Meanwhile, in a projector using color composition of RGB, each of RGBhas XYZ components, LUT data of R, G, and B may not be simply obtainedfrom the search results of X, Y, and Z, and it is necessary to perform asearch taking color mixture into consideration.

Various methods of improving luminance unevenness and color unevennessappropriate for a stack image have been suggested. For example,JP-A-2005-352171 describes a technique which calculates an intensityprofile totaled for respective light source colors (RGB) and performscolor unevenness correction such that evenness is achieved in a stackstate where a stack image (superimposed image) is displayed, instead ofperforming color unevenness correction for respective projectors.According to the technique described in JP-A-2005-352171, it is notnecessary that color unevenness is reduced for the respectiveprojectors, and it should suffice that color unevenness of a stack imageis reduced even if the individual images are uneven in color.

There is demand for power saving in an electronic apparatus, such as aprojector. Accordingly, a projector which has a dimming function ofadjusting brightness of a light source, thereby displaying an imagewhile reducing power consumption is considered.

On the other hand, unevenness correction and dimming of the light sourcemay cause degradation in brightness. These techniques are independent,and at worst, the degradation in overall brightness can be expressed bysimply multiplying a reduction ratio of brightness according to thedegree of unevenness correction, a reduction ratio of brightnessaccording to the degree of color correction, and a reduction ratio ofthe light source. For example, when brightness becomes 60% by colorcorrection, brightness becomes 70% by unevenness correction, and thelight source is reduced to 60% so as to achieve low power consumption of40%, this means that the amount of light loss of 75% (≅1-0.6×0.7×0.6) iscaused.

Focusing on brightness after color correction and dimming on a stackimage displayed by a first projector PJ1 and a second projector PJ2,even if the technique described in JP-A-2005-352171 is applied, an imagereduced through just dimming is obtained. For this reason, even if thetechnique described in JP-A-2005-352171 is applied, there is a problemin that a stack image may not be displayed with optimum light useefficiency when dimming is performed.

SUMMARY

An advantage of some aspects of the invention is that it provides animage processing method, an image processor, and an image display systemwhich can increase light use efficiency more than previously possiblewhen displaying a stack image.

(1) A first aspect of the invention is directed to an image processingmethod which performs color correction on a superimposed image obtainedby superimposing a first image formed by a first image forming unit anda second image formed by a second image forming unit. The methodincludes controlling the dimming of the first image forming unit and thesecond image forming unit on the basis of dimming rates set in the firstimage forming unit and the second image forming unit in response to agiven designated dimming rate, and performing a color correction processon image signals corresponding to the first image forming unit and thesecond image forming unit using a color correction value correspondingto the dimming rates of the first image forming unit and the secondimage forming unit.

According to this aspect of the invention, the dimming of the imageforming units is controlled on the basis of the dimming rates set in theimage forming units in response to the designated dimming rate, and thecolor correction process is performed on the image signals correspondingto the image forming units using the color correction valuecorresponding to the dimming rates of the image forming units.Therefore, it is possible to control the luminance of the light sourcesof the image forming units with different dimming rates in cooperationwith the color correction process, thereby improving the light useefficiency and displaying a brighter image with the same powerconsumption while realizing image display with a target chromaticity.

(2) A second aspect of the invention is directed to the image processingmethod according to the first aspect of the invention, wherein the colorcorrection value is a color correction value which corresponds to avalue obtained by totaling the color characteristic values of the firstimage and the second image in accordance with the dimming rates of thefirst image forming unit and the second image forming unit.

According to this aspect of the invention, the color correction valuewhich corresponds to the value obtained by totaling the colorcharacteristic values of the images to which the dimming rates of theimage forming units are applied is used, and color correction isperformed while the first image forming unit and the second imageforming unit are regarded as a single image forming unit. Accordingly,it should suffice that the color correction value common to the imageforming units is generated. For this reason, with this configuration, itis possible to achieve efficient color correction.

(3) A third aspect of the invention is directed to the image processingmethod according to the first or second aspect of the invention, whereinthe method further includes calculating a color correction target valuecorresponding to the first image forming unit and the second imageforming unit on the basis of a value obtained by totaling the colorcharacteristic values of the first image and the second image inaccordance with the dimming rates of the first image forming unit andthe second image forming unit, and generating the color correction valuecorresponding to the first image forming unit and the second imageforming unit on the basis of the color correction target valuecalculated in the calculating of the color correction target value. Inthe performing of the color correction process, the color correctionprocess may be performed using the color correction value generated inthe generating of the color correction value.

According to this aspect of the invention, the color correction targetvalue which corresponds to the image forming units is calculated on thebasis of the value obtained by totaling the color characteristic valuesof the images to which the dimming rates of the image forming units areapplied, and color correction is performed using the color correctionvalue generated on the basis of the color correction target value. Withthis configuration, it is possible to optimize color correction anddimming, to improve the light use efficiency, and to display a brighterimage with the same power consumption while realizing image display witha target chromaticity.

(4) A fourth aspect of the invention is directed to the image processingmethod according to any of the first to third aspects of the invention,wherein the method further includes calculating the dimming rates of thefirst image forming unit and the second image forming unit on the basisof the designated dimming rate and the color characteristic values ofthe first image and the second image. In the controlling of the dimming,the dimming of the first image forming unit and the second image formingunit may be performed on the basis of the dimming rates calculated inthe calculating of the dimming rates.

According to this aspect of the invention, the dimming rates of theimage forming units are calculated on the basis of the designateddimming rate and the color characteristic values of the images from theimage forming units. Therefore, it is possible to generate the dimmingrates of the image forming units in cooperation with the colorcorrection process.

(5) A fifth aspect of the invention is directed to the image processingmethod according to any of the first to fourth aspects of the invention,wherein the average value of the dimming rates of the first imageforming unit and the second image forming unit are equal to thedesignated dimming rate.

According to this aspect of the invention, it is possible to reduce theload of a process for calculating the dimming rates for obtaining theabove-described effects and to simply calculate the dimming rates.

(6) A sixth aspect of the invention is directed to the image processingmethod according to any of the first to fifth aspects of the invention,wherein the color correction process and the dimming of the first imageforming unit and the second image forming unit are performed at each ofa plurality of pixel positions within a screen to correct unevennesswithin the screen.

According to this aspect of the invention, it is possible to improve thelight use efficiency and to display a brighter image with the same powerconsumption while realizing image display with an even targetchromaticity without unevenness.

(7) A seventh aspect of the invention is provided with an imageprocessor which performs color correction on a superimposed imageobtained by superimposing a first image formed by a first image formingunit and a second image formed by a second image forming unit. The imageprocessor includes a dimming control unit that controls the dimming ofthe first image forming unit and the second image forming unit on thebasis of dimming rates set in the first image forming unit and thesecond image forming unit in response to a given designated dimmingrate, a color correction target value calculation unit that calculates acolor correction target value corresponding to the first image formingunit and the second image forming unit on the basis of a value obtainedby totaling the color characteristic values of the first image and thesecond image in accordance with the dimming rates of the first imageforming unit and the second image forming unit, and a color correctionvalue generation unit that generates a color correction valuecorresponding to the first image forming unit and the second imageforming unit on the basis of the color correction target valuecalculated by the color correction target value calculation unit.

According to this aspect of the invention, it is possible to provide animage processor which is capable of controlling the luminance of thelight sources of the image forming units with different dimming rates incooperation with the color correction process, improving the light useefficiency, and displaying a brighter image with the same powerconsumption while realizing image display with a target chromaticity.

(8) An eighth aspect of the invention is directed to the image processoraccording to the seventh aspect of the invention, wherein the imageprocessor further includes a light source luminance calculation unitthat calculates the dimming rates of the first image forming unit andthe second image forming unit on the basis of the designated dimmingrate and the color characteristic values of the first image and thesecond image. The dimming control unit may control the dimming of thefirst image forming unit and the second image forming unit on the basisof the dimming rates calculated by the light source luminancecalculation unit.

According to this aspect of the invention, the dimming rates of theimage forming unit are calculated on the basis of the designated dimmingrate and the color characteristic values of the images from the imageforming unit. Therefore, it is possible to generate the dimming rates ofthe image forming units in cooperation with the color correctionprocess.

(9) A ninth aspect of the invention is directed to an image displaysystem including the image processor according to the seventh or eighthaspect of the invention, a first image display device that has the firstimage forming unit whose dimming is controlled by the dimming controlunit and performs a color correction process on an image signalcorresponding to the first image forming unit using the color correctionvalue generated in the image processor, and a second image displaydevice that has the second image forming unit whose dimming iscontrolled by the dimming control unit and performs a color correctionprocess on an image signal corresponding to the second image formingunit using the color correction value generated in the image processor.

According to this aspect of the invention, it is possible to provide animage display system which can improve light use efficiency and displaya brighter image with the same power consumption while realizing imagedisplay with target chromaticity when displaying a stack image.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram of a configuration example of an image displaysystem according to a first embodiment of the invention.

FIG. 2 is a block diagram of a configuration example of an imageprocessor of FIG. 1.

FIG. 3 is an explanatory view of a dimming rate storage unit.

FIG. 4 is a flowchart of an example of an image process in the imagedisplay system of the first embodiment.

FIGS. 5A to 5F are diagrams showing the state of brightness when dimmingis performed after images of respective projectors subjected tounevenness correction are stacked.

FIGS. 6A to 6E are diagrams showing the state of brightness when dimmingis performed after unevenness correction is performed on a stack image.

FIGS. 7A to 7F are diagrams showing the state of brightness when dimmingis performed after images of respective projectors subjected to colorcorrection are stacked.

FIGS. 8A to 8E are diagrams showing the state of brightness when dimmingis performed after color correction is performed on a stack image.

FIG. 9A is a diagram showing an example of XYZ values of white beforeand after color correction relative to an input gradation in a firstprojector, and FIG. 9B is a diagram showing an example of LUT data whichis used for color correction in the first projector.

FIG. 10A is a diagram showing an example of XYZ values of white beforeand after color correction relative to an input gradation in a secondprojector, and FIG. 10B is a diagram showing an example of LUT datawhich is used for color correction in the second projector.

FIG. 11A is a diagram showing an example of XYZ values of white beforeand after color correction relative to an input gradation when colorcorrection is performed on a stack image, and FIG. 11B is a diagramshowing an example of LUT data which is used for color correction on astack image.

FIG. 12 is a flowchart of a process example of an image processor.

FIG. 13 is a flowchart showing a process example of a color measurementprocess in Step S1 of FIG. 12.

FIG. 14 is a flowchart showing a process example of a light sourceluminance calculation unit.

FIG. 15 is a diagram showing a calculation example of a dimming rate ina light source luminance calculation unit.

FIGS. 16A to 16H are diagrams showing the state of brightness when colorcorrection and dimming are performed under the condition of dimmingrates α=0.7 and β=0.3 according to the first embodiment.

FIG. 17A is a diagram showing an example of XYZ values of white beforeand after color correction relative to an input gradation when a stackimage of gray is displayed under the condition of dimming rates α=0.7and β=0.3, and FIG. 17B is a diagram showing an example of LUT datawhich is used for color correction of FIG. 17A.

FIG. 18 is a flowchart of an example of a color correction target valuecalculation process in Step S4 of FIG. 12.

FIG. 19 is an operation explanatory view of a color correction targetvalue calculation unit.

FIG. 20 is a block diagram of a configuration example of an imagedisplay system according to a third modification of the firstembodiment.

FIG. 21 is a block diagram of a configuration example of an imagedisplay system according to a second embodiment of the invention.

FIG. 22 is a flowchart of an example of an image process in the imagedisplay system of the second embodiment.

FIG. 23 is a flowchart of a process example of an image processoraccording to the second embodiment.

FIG. 24 is a flowchart of an example of an unevenness measurementprocess in Step S1 b of FIG. 23.

FIG. 25 is a flowchart of an example of a light source luminancecalculation process in Step S3 b of FIG. 23.

FIG. 26 is an explanatory view of an example of a light source luminancecalculation process according to the second embodiment.

FIG. 27 is a diagram showing a calculation example of a dimming rate bya light source luminance calculation unit according to the secondembodiment.

FIG. 28A is a diagram showing an example of a change in luminance in ahorizontal direction of a screen, and FIG. 28B is a diagramschematically showing the change in luminance of FIG. 28A in a stepwisemanner.

FIG. 29 is an explanatory view of a general color correction principle.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detailwith reference to the drawings. The following embodiments do not undulylimit the contents of the invention described in the appended claims.Also, not all of configurations described below are constituent featuresessential for solving the problems of the invention.

Although in the following embodiments, an example where a stack image isdisplayed using two projectors (in a broad sense, image display devices)will be described, the invention may be applied to a case where a stackimage is displayed using three or more projectors.

First Embodiment

FIG. 1 is a block diagram of a configuration example of an image displaysystem according to a first embodiment of the invention.

An image display system 10 displays a stack image, which is generated bysuperimposing a plurality of images projected from a plurality ofprojectors, on a screen SCR. The image display system 10 includes afirst projector (first image display device) PJ1, a second projector(second image display device) PJ2, an image processor 100, an imagesignal supply device 200, and an operating unit 210. In order to achievethe optimization of color correction and dimming, the image displaysystem 10 also includes a color measurement device 300 and a sensor 400.The operating unit 210 may be provided in the image processor 100, thefirst projector PJ1 or the second projector PJ2. Some or all of thefunctions of the image processor 100 may be provided in the firstprojector PJ1 or the second projector PJ2.

The first projector PJ1 includes a first image forming unit (not shown),and projects an image (first image) formed by the first image formingunit on the basis of an input image signal on the screen SCR. The firstimage forming unit includes a light source, an optical system(illumination optical system) which sends light from the light source toan optical modulator, a dichroic mirror, an optical modulator, such as aliquid crystal light valve, a color synthesis prism (X prism), aprojection optical system, a driving circuit, and the like. The firstimage forming unit modulates and synthesizes the color components oflight from the light source on the basis of the input image signal usingthe optical modulator and projects light after synthesis on the screenSCR through a projection lens. The first projector PJ1 is configuredsuch that luminance is adjusted on the basis of a dimming control signalfrom the image processor 100. Similarly, the second projector PJ2includes a second image forming unit (not shown) and projects an image(second image) formed by the second image forming unit on the basis ofan input image signal on the screen SCR. The second projector PJ2 isconfigured such that luminance is adjusted on the basis of a dimmingcontrol signal from the image processor 100. At this time, theprojectors are arranged such that the image projected from the secondprojector PJ2 is superimposed on the image projected from the firstprojector PJ1 on the screen SCR. Accordingly, a stack image(superimposed image) in which the images from the projectors aresuperimposed is displayed. The configuration of the second projector PJ2is the same as the configuration of the first projector PJ1.

The image processor 100 generates a color correction value which is usedto perform a color correction process corresponding to each projector onthe input image signal in accordance with a designated dimming rate andcontrols the dimming of at least one of the first projector PJ1 and thesecond projector PJ2.

The image signal supply device 200 is a DVD (Digital Versatile Disc)device, a personal computer (PC), or the like, and supplies the imagesignal to the first projector PJ1 and the second projector PJ2. When thecolor correction process is performed in the image processor 100, theimage signal supply device 200 supplies an image signal to the imageprocessor 100. The image signal supply device 200 can supply an imagesignal corresponding to a measurement pattern during color measurementdescribed below to the image processor 100. As the measurement pattern,a gray image in which the color components of RGB have the samegradation value, a RGB color solid image which has only the gradationvalue of one color component of RGB (the gradation values of other colorcomponents are 0), a patch image in which only a rectangular measurementregion changes in color, or the like is used.

The operating unit 210 is an operation panel which is provided todesignate the light source luminance of the first projector PJ1 and thesecond projector PJ2. The user can designate a dimming rate (forexample, 50%) through the operating unit 210 or can designate one fromamong dimming rates set in advance. User's operation information throughthe operating unit 210 corresponds to a designated dimming rate and isinput to the image processor 100.

The color measurement device 300 is a point measurement colorimeter andis arranged so as to measure the color of a measurement region within animage projected on the screen SCR. The function of the color measurementdevice 300 is realized by a spectroradiometer (for example, PR-705manufactured by Photo Research, or the like) which includes a prismspectroscope and a linear array sensor. The color measurement device 300may be realized by a colorimeter (for example, CL-200 manufactured byKonica Minolta, or the like) which includes an XYZ filter and aphotocell. The color measurement device 300 captures the above-describedgray image, solid image, or patch image displayed on the screen SCR byeach projector when color measurement is performed. The colormeasurement device 300 acquires XYZ tristimulus values of the CIE 1931colorimetric system as color characteristic values. The colormeasurement values acquired by the color measurement device 300 for therespective projectors are sent to the image processor 100 as colorcharacteristic values. The measurement process in the color measurementdevice 300 may be performed under the control of the image processor100. The function of the color measurement device 300 may be realized byusing a measurement value at a measurement position from an in-planeintensity distribution (unevenness measurement values) measured by aknown unevenness measurement device.

The sensor 400 detects the brightness, temperature, or the like of thevisual environment, and sensor information corresponding to thedetection result is input to the image processor 100. The imageprocessor 100 acquires the designated dimming rate using the operationinformation from the operating unit 210 or the sensor information fromthe sensor 400.

The image processor 100 obtains a color correction target value of theimage forming units on the basis of the dimming rates of the projectorscorresponding to the designated dimming rate and the color measurementvalues of the images from the projectors acquired by the colormeasurement device 300, and obtains a color correction valuecorresponding to the color correction target value. The image processor100 supplies the color correction value to the first projector PJ1 andthe second projector PJ2 which perform the color correction process. Atthis time, the image processor 100 forcibly performs dimming control ofthe first projector PJ1 and the second projector PJ2 with the dimmingrates of the projectors corresponding to the designated dimming ratedesignated by the operation information. Alternatively, the imageprocessor 100 performs dimming control of the first projector PJ1 andthe second projector PJ2 with the dimming rates of the projectorscorresponding to the designated dimming rate determined on the basis ofthe sensor information from the sensor 400. Accordingly, the display ofthe target chromaticity is realized and the light use efficiencyincreases.

The image processor 100 can have a central processing unit (hereinafter,referred to as CPU) and a memory (not shown). In this case, the CPUreads a program stored in the memory and performs a processcorresponding to the program, thereby realizing the above-describedcolor correction process and dimming control. Alternatively, thefunction of the image processor 100 may be realized by a logic circuit,such as an ASIC (Application Specific Integrated Circuit).

Image Processor

FIG. 2 is a block diagram of a configuration example of the imageprocessor 100 of FIG. 1. FIG. 2 shows the image signal supply device200, the operating unit 210, the color measurement device 300, thesensor 400, the first projector PJ1, and the second projector PJ2 inaddition to the image processor 100. In FIG. 2, the same portions asthose in FIG. 1 are represented by the same reference numerals, anddescriptions thereof will not be repeated.

The image processor 100 includes a color correction value calculationunit 110, a dimming rate calculation unit 120, a dimming rate storageunit 130, and a dimming control unit 140. The color correction valuecalculation unit 110 includes a color correction target valuecalculation unit 112 and a color correction look-up table (hereinafter,referred to as LUT) generation unit 114. The dimming rate calculationunit 120 includes a designated dimming rate generation unit 122 and alight source luminance calculation unit 124.

The color correction value calculation unit 110 generates a colorcorrection value corresponding to the dimming rates of the projectors(specifically, the image forming units), and generates a colorcorrection LUT in which color correction values are tabulated. The colorcorrection target value calculation unit 112 calculates a colorcorrection target value. The color correction target value is generatedon the basis of the dimming rates of the projectors (or the designateddimming rate) and color measurement values of the images from theprojectors acquired by the color measurement device 300. The colorcorrection LUT generation unit 114 generates the color correction valueon the basis of the color correction target value by the colorcorrection target value calculation unit 112. The color correction valuegenerated by the color correction LUT generation unit 114 is stored inthe first projector PJ1 and the second projector PJ2.

The dimming rate calculation unit 120 calculates the dimming ratescorresponding to the projectors from the designated dimming rate. Thedesignated dimming rate generation unit 122 generates a designateddimming rate δ corresponding to a target light source luminance from theoperation information from the operating unit 210 or the sensorinformation from the sensor 400. The light source luminance calculationunit 124 calculates the target luminance of the projectors as dimmingrates α and β on the basis of the designated dimming rate generated bythe designated dimming rate generation unit 122 and the colormeasurement values of the projectors input from the color measurementdevice 300. The dimming rates α and β of the projectors calculated bythe light source luminance calculation unit 124 are stored in thedimming rate storage unit 130 in association with the designated dimmingrate δ.

The dimming rate storage unit 130 stores the dimming rates obtained forthe projectors (the image forming units in the image display devices) inresponse to the designated dimming rate based on the operationinformation from the operating unit 210 or the sensor information fromthe sensor 400.

FIG. 3 is an explanatory view of the dimming rate storage unit 130.

Prior to the color correction process in the first embodiment, thedimming rates for the projectors are obtained in accordance with thedesignated dimming rate shown in FIG. 3, and the dimming rate storageunit 130 stores the dimming rates α and β for the projectors in responseto the designated dimming rate δ. For example, when δ1 is designated asthe designated dimming rate by the operation information from theoperating unit 210 or the sensor information from the sensor 400, thedimming rate storage unit 130 is configured such that dimming rates α1and β1 which are stored in response to the designated dimming rate δ1are referenced.

Referring to FIG. 2, the dimming control unit 140 controls the dimmingof the projectors with the dimming rates of the projectors correspondingto the designated dimming rate stored in the dimming rate storage unit130. For this reason, the dimming control unit 140 outputs dimmingcontrol signals for controlling the luminance of the light sources ofthe projectors to the projectors.

The first projector PJ1 includes a first color correction LUT storageunit (first color correction value storage unit) 160, a first colorcorrection processing unit 162, and a first image forming unit 164. Thesecond projector PJ2 includes a second color correction LUT storage unit(second color correction value storage unit) 170, a second colorcorrection processing unit 172, and a second image forming unit 174.

The first color correction LUT storage unit 160 stores a plurality ofcolor correction LUTs generated in response to the designated dimmingrate in the color correction value calculation unit 110. The first colorcorrection LUT storage unit 160 selects a color correction LUTcorresponding to the designated dimming rate δ designated from thedimming rate calculation unit 120 from among a plurality of colorcorrection LUTs. The first color correction processing unit 162 performsthe color correction process on an image signal corresponding to thefirst projector PJ1 using the color correction values of the colorcorrection LUT selected in the first color correction LUT storage unit160. The color correction LUT prepares correction values correspondingto the correction amount (ΔKRij, ΔKGij, ΔKBij) of a gradation value Kij(for example, gray gradation value) at a pixel position (i, j) in animage for every pixel position and every gradation value. The pixelvalues (Rij′, Gij′, Bij′) of an image signal after correction in thefirst color correction processing unit 162 relative to the pixel values(Rij, Gij, Bij) at the pixel position (i,j) of the input image signalare as follows.

Rij′=Rij+ΔKRij  (1)

Gij′=Gij+ΔKGij  (2)

Bij′=Bij+ΔKBij  (3)

As described above, the first color correction processing unit 162performs the color correction process on the basis of the input imagesignal from the image signal supply device 200 with reference to thecolor correction LUT in accordance with the in-plane position andgradation of the image. At this time, the first color correctionprocessing unit 162 performs the color correction process whileinterpolating between the lattice points of the color correction LUT byknown linear interpolation or the like. The image signal subjected tothe color correction process corresponding to the first projector PJ1 inthe first color correction processing unit 162 is output to the firstimage forming unit 164. The first image forming unit 164 modulates thecolor components of light from the light source, which is dimmed on thebasis of the dimming control signal from the dimming control unit 140,using the optical modulator on the basis of the image signal subjectedto the color correction process in the first color correction processingunit 162, and projects light on the screen SCR through the projectionlens.

In the second projector PJ2, similarly to the first projector PJ1, thesecond color correction LUT storage unit 170 stores the color correctionLUT, and the second color correction processing unit 172 performs thecolor correction process on the input image signal. The second imageforming unit 174 modulates the color components of light from the lightsource, which is dimmed on the basis of the dimming control signal fromthe dimming control unit 140, using the optical modulator on the basisof the image signal subjected to the color correction process in thesecond color correction processing unit 172, and projects light on thescreen SCR through the projection lens.

FIG. 4 is a flowchart of an example of an image process in the imagedisplay system 10 of the first embodiment. Although the image processshown in FIG. 4 is performed in the image processor 100, the firstprojector PJ1, and the second projector PJ2, the overall process may beperformed in the image processor 100.

First, the image processor 100 receives the operation information fromthe operating unit 210 or the sensor information of the sensor 400 toreceive the designated dimming rate (Step S100). The image processor 100may perform a process for determining the designated dimming rate on thebasis of the operation information from the operating unit 210 or thesensor information from the sensor 400.

Next, the dimming control unit 140 controls the dimming of the imageforming units with the dimming rates set in the image forming units(projectors) in response to the designated dimming rate received in StepS100 with reference to the dimming rate storage unit 130 (Step S102).That is, in Step S102, as a dimming control step, the dimming controlunit 140 controls the dimming of the first image forming unit and thesecond image forming unit on the basis of the dimming rates set in thefirst image forming unit and the second image forming unit in responseto the designated dimming rate.

Each projector includes the color correction LUT storage unit, andperforms the color correction process on the image signal correspondingto the projector using the color correction value corresponding to thedimming rate of the corresponding image forming unit in Step S102 (StepS104). That is, in Step S104, as a color correction process step, thecolor correction process is performed on the image signals correspondingto the first image forming unit and the second image forming unit usingthe color correction value corresponding to the dimming rates of thefirst image forming unit and the second image forming unit. Steps S102and S104 may be reversed. In each projector, the image signal subjectedto the color correction process in Step S104 is supplied to thecorresponding image forming unit (Step S106), and a sequence ofprocesses ends (end).

In this way, through the cooperation with the color correction processwhich realizes display of a stack image with a target chromaticity, itis possible to adjust the luminance of the light source of eachprojector with a dimming rate different from the designated dimmingrate. As a result, it is possible to increase the light use efficiencywithout wastefully decreasing the luminance of the light source.

Comparative Example

Brightness after unevenness correction and dimming on a stack imagedisplayed by the first projector PJ1 and the second projector PJ2 isconsidered.

FIGS. 5A to 5F show the state of brightness when dimming is performedafter the images of the respective projectors subjected to unevennesscorrection are stacked. FIGS. 5A to 5F schematically show a change inluminance in the horizontal direction of the screen in a stepwise manneras in FIG. 28B. In FIGS. 5A to 5F, the horizontal axis represents thepixel position of the screen and the vertical axis represents luminance(in a broad sense, intensity).

As shown in FIGS. 5A and 5B, the first projector PJ1 and the secondprojector PJ2 have unevenness, and it is assumed that the minimum valueof the luminance of the first projector PJ1 is 60 and the minimum valueof the luminance of the second projector PJ2 is 40. At this time, withregard to the first projector PJ1, unevenness correction is performed inaccordance with the minimum value 60 of the luminance, and the luminanceafter unevenness correction is as shown in FIG. 5C. Similarly, withregard to the second projector PJ2, unevenness correction is performedin accordance with the minimum value of the luminance, and the luminanceafter unevenness correction is as shown in FIG. 51D. If a stack image isdisplayed using an image of the first projector PJ1 and an image of thesecond projector PJ2 after unevenness correction, as shown in FIG. 5E,the luminance of both projectors is totaled, and a bright stack imagewith luminance of 100 is displayed. In this state, if the light sourcesof both projectors are reduced to 50%, as shown in FIG. 5F, a stackimage with luminance of 50 is displayed.

Meanwhile, as described in JP-A-2005-352171, a case where unevennesscorrection is performed after a stack image is displayed, and dimming isperformed is considered.

FIGS. 6A to 6E show the state of brightness when dimming is performedafter unevenness correction is performed on a stack image. FIGS. 6A to6E schematically show a change in luminance in the horizontal directionof the screen in a stepwise manner as in FIG. 28B. In FIGS. 6A to 6E,the horizontal axis represents the pixel position of the screen and thevertical axis represents luminance.

FIG. 6A schematically shows a change in luminance of an image of thefirst projector PJ1 which is the same as in FIG. 5A. FIG. 6Bschematically shows a change in luminance of an image of the secondprojector PJ2 which is the same as in FIG. 5B. As shown in FIG. 6C, astack image using the image of FIG. 6A and the image of FIG. 6B hasunevenness in which the minimum value of the luminance is 140 (=100+40).At this time, unevenness correction is performed on the stack image inaccordance with the minimum value 140 of the luminance, and afterunevenness correction, the result is shown in FIG. 6D. In this state, ifthe light sources of both projectors are reduced to 50%, as shown inFIG. 6E, a stack image with luminance of 70 is displayed.

When comparing the image of FIG. 5F with the image of FIG. 6E, the imageof FIG. 6E is a brighter image. However, the image of FIG. 6E isobtained by reducing the image of FIG. 6D, and the efficiency whendimming is performed is not optimum.

Next, brightness when dimming is performed after color correction isperformed on a stack image displayed by the first projector PJ1 and thesecond projector PJ2 is considered.

If a target characteristic is set in sRGB (a gradation characteristic inwhich white point chromaticity is D65 and gamma is 2.2) or the like, thetarget balance of X, Y, and Z is uniquely set. If the balance of X, Y,and Z in the intrinsic characteristic of the projector is different fromthe balance of X, Y, and Z in sRGB, the balance is achieved based on therelatively smallest component. For this reason, while wasteful light useefficiency occurs, when dimming is performed after color correction isperformed on a stack image, there is the possibility of improvement.

FIGS. 7A to 7F show the state of brightness when dimming is performedafter the images of the projectors subjected to color correction arestacked. In FIGS. 7A to 7F, the horizontal axis represents an inputvoltage and the vertical axis represents XYZ values.

It is assumed that the first projector PJ1 has a characteristic with thebalance of X, Y, and Z shown in FIG. 7A and the second projector PJ2 hasa characteristic with the balance of X, Y, and Z shown in FIG. 7B. Asshown in FIG. 7A, with regard to the first projector PJ1, since X is toosmall, the brightness after color correction is degraded accordingly(FIG. 7C). Similarly, as shown in FIG. 7B, with regard to the secondprojector PJ2, since Y is too small, brightness after color correctionis degraded accordingly (FIG. 7D). For this reason, if the images fromthe first projector PJ1 and the second projector PJ2 after colorcorrection are stacked (FIG. 7E) and dimmed to 50%, as shown in FIG. 7F,a dark image is obtained.

Meanwhile, as described in JP-A-2005-352171, a case where colorcorrection is performed after a stack image is displayed, and dimming isperformed is considered.

FIGS. 8A to 8E show the state of brightness when dimming is performedafter color correction is performed on a stack image. In FIGS. 8A to 8E,the horizontal axis represents an input voltage and the vertical axisrepresents XYZ values.

It is assumed that the first projector PJ1 has a characteristic with thebalance of X, Y, and Z shown in FIG. 8A, and the second projector PJ2has a characteristic with the balance of X, Y, and Z shown in FIG. 8B. Astack image using the image of FIG. 8A and the image of FIG. 8B becomesa bright image shown in FIG. 8C. Meanwhile, if color correction isperformed, an image after color correction is as shown in FIG. 8D. Inthis state, if the light sources of both projectors are reduced to 50%,as shown in FIG. 8E, a stack image is displayed.

When comparing the image of FIG. 7F with the image of FIG. 8E, thebalance of X, Y, and Z before color correction is improved and reaches aproportion close to a target balance, thereby reducing degradation inbrightness due to color correction. Thus, the image of FIG. 8E becomes abright image. From this point, it is understood that, for example, evenwhen focusing on LUT data which is used for color correction in eachprojector, while the light use efficiency is not sufficient, the lightuse efficiency in the image of FIG. 8E increases slightly.

FIG. 9A shows an example of XYZ values of white before and after colorcorrection relative to an input gradation in the first projector PJ1.FIG. 9B shows an example of LUT data which is used for color correctionin the first projector PJ1. The result of color correction using the LUTdata of FIG. 9B is as shown in FIG. 7C.

FIG. 10A shows an example of XYZ values of white before and after colorcorrection relative to an input gradation in the second projector PJ2.FIG. 10B shows an example of LUT data which is used for color correctionin the second projector PJ2. The result of color correction using theLUT data of FIG. 10B is as shown in FIG. 7D.

FIG. 11A shows an example of XYZ values of white before and after colorcorrection relative to an input gradation when color correction isperformed on a stack image. FIG. 11B shows an example of LUT data whichis used for color correction on a stack image. The result of colorcorrection using the LUT data of FIG. 11B is as shown in FIG. 8D. FIG.11A shows an example of XYZ values of white before and after colorcorrection in a state of being reduced to 50%.

As shown in FIG. 9B, in the first projector PJ1, since R from among RGBis especially dark, with regard to R, color correction is performedusing the substantially entire range of LUT data prepared in advancecompared to GB. As shown in FIG. 10B, in the second projector PJ2, sinceG from among RGB is especially dark, with regard to G, color correctionis performed using the substantially entire range of LUT data preparedin advance compared to RB. When comparing FIG. 9B and FIG. 10B, thesecond projector PJ2 displays an image with available capacity for RBcompared to the first projector PJ1. Meanwhile, as shown in FIG. 11B, inthe stack image, the use efficiency of LUT data of R is slightlyimproved compared to FIG. 10B. Accordingly, it is thought that the imageof FIG. 8E has light use efficiency higher than the image of FIG. 7F.

However, in the case of color correction, similarly to unevennesscorrection, the image of FIG. 8E is obtained by simply reducing theimage of FIG. 8D, and the efficiency when dimming is performed is notoptimum. For this reason, according to the technique described inJP-A-2005-352171, an image which is reduced through just dimming isobtained, and a stack image may not be displayed with the optimum lightuse efficiency when dimming is performed. That is, according to thetechnique described in JP-A-2005-352171, it is difficult to increase thelight use efficiency by displaying an image as brightly as possible withthe same power consumption or displaying an image with the samebrightness with as low power consumption as possible. Accordingly, inthe first embodiment, through the cooperation with the color correctionprocess which realizes display of a stack image with a targetchromaticity, it is possible to adjust the luminance of the light sourceof each projector with a dimming rate different from the designateddimming rate, thereby increasing the light use efficiency withoutwastefully decreasing the luminance of the light source.

Process Example

Hereinafter, a process example of the image processor 100 will bespecifically described.

FIG. 12 is a flowchart of a process example of the image processor 100.

FIG. 13 is a flowchart of a process example of a color measurementprocess in Step S1 of FIG. 12.

When the image processor 100 realizes the process of FIG. 12 or 13through a software process, a program which realizes the followingprocess is stored in the memory which is embedded in the image processor100, and the CPU which reads the program performs a processcorresponding to the program.

First, the image processor 100 controls the color measurement device 300and acquires the XYZ values of the screen center, which is themeasurement result of the color measurement device 300, as the colormeasurement values of the projectors (Step S1).

In Step S1, first, each projector projects one of the solid images ofthe entire screen of the respective gradations of RGB colors on thescreen SCR (Step S11). In this state, the image processor 100 performscontrol for measuring the XYZ values of the screen center using thecolor measurement device 300 and acquires the XYZ values as themeasurement result (Step S12). Thereafter, when the entire measurementdoes not end (Step S13: N), the image processor 100 returns to Step S11and projects the next solid image on the screen SCR. In this way, if thecolor measurement values are acquired for all the solid images of theentire screen of the respective gradations of the RGB colors (Step S13:Y), the image processor 100 ends the processing of Step S1 (end).

Subsequently, the image processor 100 obtains the target light sourceluminance from the operation information from the operating unit 210 orthe sensor information from the sensor 400 in the designated dimmingrate generation unit 122, and sets the designated dimming, rate δcorresponding to the target light source luminance (Step S2).

The image processor 100 calculates the light source luminance of theprojectors from the XYZ values of white and the target light sourceluminance (=designated dimming rate δ) in the light source luminancecalculation unit 124, and obtains the dimming rates α and βcorresponding to the light source luminance (Step S3). That is, in StepS3, as a light source luminance calculation step, the light sourceluminance calculation unit 124 calculates the dimming rates α and β ofthe first image forming unit and the second image forming unit on thebasis of the designated dimming rate δ and the color characteristicvalues of the first image and the second image.

Next, the image processor 100 calculates the color correction targetvalue in a stack state for each gradation from the light sourceluminance of each projector and the color measurement value of eachgradation of each projector acquired in Step S1 in the color correctiontarget value calculation unit 112 (Step S4). That is, in Step S4, as acolor correction target value calculation step, the color correctiontarget value calculation unit 112 calculates the color correction targetvalue corresponding to the first image forming unit and the second imageforming unit on the basis of a value obtained by totaling the colorcharacteristic values of the first image and the second image inaccordance with the dimming rates of the first image forming unit andthe second image forming unit.

Thereafter, the image processor 100 generates the color correction LUTon the basis of the color correction target value in the colorcorrection LUT generation unit 114 (Step S5). That is, in Step S5, as acolor correction value generation step, the color correction LUTgeneration unit 114 generates the color correction value correspondingto the image forming units on the basis of the color correction targetvalue calculated in Step S4.

The color correction LUT generated in Step S5 is stored to the colorcorrection LUT storage unit of each projector. Subsequently, the imageprocessor 100 performs dimming control of the projectors with thedimming rates calculated in Step S3, and the projectors perform thecolor correction process with reference to the color correction LUTgenerated in Step S5.

Next, the light source luminance calculation process in Step S3 andcolor correction target value calculation process in Step S4 of FIG. 12will be specifically described.

Light Source Luminance Calculation Process

It is assumed that the XYZ values of the RGB primary colors of the firstprojector PJ1 are (X_(R)1, Y_(R)1, Z_(R)1), (X_(G)1, Y_(G)1, Z_(G)1),and (X_(B)1, Y_(B)1, Z_(B)1). Similarly, the XYZ values of the RGBprimary colors of the second projector PJ2 are (X_(R)2, Y_(R)2, Z_(R)2),(X_(G)2, Y_(G)2, Z_(G)2), and (X_(B)2, Y_(B)2, Z_(B)2). In general, theXYZ values when the RGB primary colors are input to the first projectorPJ1 and the second projector PJ2 are expressed by Expression (4).

$\begin{matrix}{\begin{bmatrix}X \\Y \\Z\end{bmatrix} = {\begin{bmatrix}{{X_{R}1} + {X_{R}2}} & {{X_{G}1} + {X_{G}2}} & {{X_{B}1} + {X_{B}2}} \\{{Y_{R}1} + {Y_{R}2}} & {{Y_{G}1} + {Y_{G}2}} & {{Y_{B}1} + {Y_{B}2}} \\{{Z_{R}1} + {Z_{R}2}} & {{Z_{G}1} + {Z_{G}2}} & {{Z_{B}1} + {Z_{B}2}}\end{bmatrix}\begin{bmatrix}R \\G \\B\end{bmatrix}}} & (4)\end{matrix}$

The above expression corresponds to the XYZ values of a solid image ofwhite in a stack state. Accordingly, when the target XYZ values of sRGBor the like are Xt, Yt, and Zt,Yt=Y_(R)1+Y_(R)2+Y_(G)1+Y_(G)2+Y_(B)1+Y_(B)2 is set using the aboveexpression, and Xt and Zt in sRGB are obtained on the basis of thechromaticity of sRGB and Yt. If a target dimming rate is 6 (0≦δ≦1), theXYZ values (Xc,Yc,Zc) after color correction and dimming are expressedby Expressions (5-1) to (5-3). In the following expressions, one of Rc,Gc, and Bc becomes equal to 1. Since a color component which becomesequal to 1 has weak luminance, it is necessary that the correspondingcolor component is emitted fully so as to match the color to targetwhite. When a color component which does not become equal to has strongluminance, it should suffice that the corresponding color component isemitted weakly.

$\begin{matrix}{\begin{bmatrix}R_{t} \\G_{t} \\B_{t}\end{bmatrix} = {\begin{bmatrix}{{X_{R}1} + {X_{R}2}} & {{X_{G}1} + {X_{G}2}} & {{X_{B}1} + {X_{B}2}} \\{{Y_{R}1} + {Y_{R}2}} & {{Y_{G}1} + {Y_{G}2}} & {{Y_{B}1} + {Y_{B}2}} \\{{Z_{R}1} + {Z_{R}2}} & {{Z_{G}1} + {Z_{G}2}} & {{Z_{B}1} + {Z_{B}2}}\end{bmatrix}^{- 1}\begin{bmatrix}X_{t} \\Y_{t} \\Z_{t}\end{bmatrix}}} & \left( {5\text{-}1} \right) \\\begin{matrix}{R_{c} = {R_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}} \\{G_{c} = {G_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}} \\{B_{c} = {B_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}}\end{matrix} & \left( {5\text{-}2} \right) \\{\begin{bmatrix}X_{c} \\Y_{c} \\Z_{c}\end{bmatrix} = {\delta \times {\begin{bmatrix}{{X_{R}1} + {X_{R}2}} & {{X_{G}1} + {X_{G}2}} & {{X_{B}1} + {X_{B}2}} \\{{Y_{R}1} + {Y_{R}2}} & {{Y_{G}1} + {Y_{G}2}} & {{Y_{B}1} + {Y_{B}2}} \\{{Z_{R}1} + {Z_{R}2}} & {{Z_{G}1} + {Z_{G}2}} & {{Z_{B}1} + {Z_{B}2}}\end{bmatrix}\begin{bmatrix}R_{c} \\G_{c} \\B_{c}\end{bmatrix}}}} & \left( {5\text{-}3} \right)\end{matrix}$

Meanwhile, in the first embodiment, the dimming rates are determined incooperation with color correction, thereby making the dimming rates ofthe projectors different from each other. If the dimming rate of thefirst projector PJ1 is α (0≦α≦1) and the dimming rate of the secondprojector PJ2 is β (0β≦1), the light source luminance calculation unit124 obtains the XYZ values (Xp,Yp,Zp) after color correction and dimmingin accordance with Expressions (6-1) to (6-3).

$\begin{matrix}{\begin{bmatrix}R_{t} \\G_{t} \\B_{t}\end{bmatrix} = {\begin{bmatrix}{{\alpha \; X_{R}1} + {\beta \; X_{R}2}} & {{\alpha \; X_{G}1} + {\beta \; X_{G}2}} & {{\alpha \; X_{B}1} + {\beta \; X_{B}2}} \\{{\alpha \; Y_{R}1} + {\beta \; Y_{R}2}} & {{\alpha \; Y_{G}1} + {\beta \; Y_{G}2}} & {{\alpha \; Y_{B}1} + {\beta \; Y_{B}2}} \\{{\alpha \; Z_{R}1} + {\beta \; Z_{R}2}} & {{\alpha \; Z_{G}1} + {\beta \; Z_{G}2}} & {{\alpha \; Z_{B}1} + {\beta \; Z_{B}2}}\end{bmatrix}^{- 1}\begin{bmatrix}X_{t} \\Y_{t} \\Z_{t}\end{bmatrix}}} & \left( {6\text{-}1} \right) \\\begin{matrix}{R_{p} = {R_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}} \\{G_{p} = {G_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}} \\{B_{p} = {B_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}}\end{matrix} & \left( {6\text{-}2} \right) \\{\begin{bmatrix}X_{p} \\Y_{p} \\Z_{p}\end{bmatrix} = {\begin{bmatrix}{{\alpha \; X_{R}1} + {\beta \; X_{R}2}} & {{\alpha \; X_{G}1} + {\beta \; X_{G}2}} & {{\alpha \; X_{B}1} + {\beta \; X_{B}2}} \\{{{\alpha Y}_{R}1} + {\beta \; Y_{R}2}} & {{\alpha \; Y_{G}1} + {\beta \; Y_{G}2}} & {{\alpha \; Y_{B}1} + {\beta \; Y_{B}2}} \\{{{\alpha Z}_{R}1} + {\beta \; Z_{R}2}} & {{\alpha \; Z_{G}1} + {\beta \; Z_{G}2}} & {{\alpha \; Z_{B}1} + {\beta \; Z_{B}2}}\end{bmatrix}\begin{bmatrix}R_{p} \\G_{p} \\B_{p}\end{bmatrix}}} & \left( {6\text{-}3} \right)\end{matrix}$

In Expressions (6-1) to (6-3), it is assumed that δ=(α+β)/2. That is,the dimming rates α and β are obtained such that the designated dimmingrate δ becomes equal to the average value of the dimming rate α of thefirst projector PJ1 and the dimming rate β of the second projector PJ2.The light source luminance calculation unit 124 obtains the dimmingrates α and β through the following process.

FIG. 14 is a flowchart of a process example of the light sourceluminance calculation unit 124. When the image processor 100 includingthe light source luminance calculation unit 124 realizes the process ofFIG. 14 through a software process, a program which realizes thefollowing process is stored in the memory which is embedded in the imageprocessor 100, and the CPU which reads the program performs a processcorresponding to the program. The process of FIG. 14 is performed inStep S3 of FIG. 12.

First, prior to searching the dimming rates α and β, the light sourceluminance calculation unit 124 performs the initial settings of thedimming rates α and β corresponding to the light source luminance andthe luminance Yp after dimming (Step S31). As the initial setting of thelight source luminance, while α=β=δ may be set as an initial value, forexample, α=0 and β=2δ are set, a is changed in an increasing directionand β is changed in a decreasing direction to simplify a search process.As the initial setting of the luminance Yp after dimming, 0 is set.

Next, the light source luminance calculation unit 124 obtains the valueof the right side of Expression (6-3) using the dimming rates α and βand sets the value to a variable Yq (Step S32).

Subsequently, the light source luminance calculation unit 124 comparesYp with Yq obtained in Step S32 (Step S33). When Yq is greater than Yp(Step S33: Y), the light source luminance calculation unit 124 updatesthe dimming rates α and β corresponding to Yq as the optimum lightsource luminance and substitutes Yq into the luminance Yp after dimming(Step S34).

When all the combinations of the light source luminance do not end (StepS35: N), the dimming rates α and β are updated (Step S36), and theprocess returns to Step S32. Step S36 is not limited to a step ofchanging the dimming rates, and it is desirable to set the dimming ratestaking into consideration the processing time or the like. In Step S36,for example, the dimming rates are changed to (α,β)=(0,1),(α,β)=(0.05,0.95), (α,β)=(0.10,0.90), . . . , (α,β)=(0.95,0.05), and(α,β)=(1,0).

In Step S35, when all the combinations of the light source luminance end(Step S35: Y), the light source luminance calculation unit 124 ends asequence of processes (end), and determines the dimming rates α and β atthat time as the light source luminance of the projectors.

FIG. 15 shows a calculation example of the dimming rates α and β in thelight source luminance calculation unit 124. FIG. 15 shows a predictedluminance ratio during uneven dimming relative to luminance during evendimming (α=β=0.5) when the color characteristic of the first projectorPJ1 is as shown in FIG. 9A and the color characteristic of the secondprojector PJ2 is as shown in FIG. 10A. In FIG. 15, the horizontal axisrepresents a and the vertical axis represents a predicted luminanceratio.

FIG. 15 shows a case where the dimming rates α and β are different fromeach other based on even dimming, thereby further increasing theluminance after color correction and dimming. In this case, when thedimming rates α=0.7 and β=0.3, the predicted luminance ratio is maximal.

FIGS. 16A to 16H show the state of brightness when color correction anddimming are performed under the condition of the dimming rates α=0.7 andβ=0.3 according to the first embodiment. In FIGS. 16A to 16H, thehorizontal axis represents an input voltage and the vertical axisrepresents an XYZ value.

It is assumed that the first projector PJ1 has a characteristic with thebalance of X, Y, and Z shown in FIG. 16A, and the second projector PJ2has a characteristic with the balance of X, Y, and Z shown in FIG. 16B.If color correction is performed, a stack image using the image of FIG.16A and the image of FIG. 16B is as shown in FIG. 16C. In this state, ifthe light sources of both projectors are reduced to 50%, as shown inFIG. 16D, a stack image is displayed.

Meanwhile, if the image shown in FIG. 16A is reduced to 70% with thedimming rate α=0.7, an image shown in FIG. 16E is obtained. If the imageshown in FIG. 16B is reduced to 30% with the dimming rate β=0.3, animage shown in FIG. 16F is obtained. A stack image of the image of FIG.16E and the image of FIG. 16F is as shown in FIG. 16G, and if colorcorrection is performed, an image shown in FIG. 16H is obtained. Whencomparing the image of FIG. 16D with the image of FIG. 16H, in the imageof FIG. 16H, the XYZ values after correction are further increased,thereby suppressing degradation in luminance after correction.

FIG. 17A shows an example of XYZ values of white before and after colorcorrection relative to an input gradation when a stack image of gray isdisplayed under the condition of the dimming rates α=0.7 and β=0.3. FIG.17B shows an example (LUT data of G and B are superimposed) of LUT datawhich is used for color correction of FIG. 17A.

When comparing FIG. 17A and FIG. 11A in which color correction isperformed on a stack image, FIG. 17A shows that the XYZ values aftercorrection are further increased, thereby suppressing degradation inluminance after correction. In particular, when comparing FIG. 17B andFIG. 11B, LUT data is a value closer to a maximum value 1023, and thelight use efficiency is rising. Accordingly, when images from twoprojectors are superimposed to brighten an image, if it is assumed thatpower consumption or brightness during projection is simply inproportion to the amount of light of the light source, according to thefirst embodiment, brightness can be raised with the same powerconsumption.

Color Correction Target Value Calculation Process

The color correction target value calculation unit 112 calculates thecolor correction target value in each gradation on the basis of thedimming rate corresponding to the light source luminance calculated bythe light source luminance calculation unit 124 and the colormeasurement value obtained from the color measurement device 300.

FIG. 18 is a flowchart of an example of a color correction target valuecalculation process in Step S4 of FIG. 12. When the image processor 100realizes the process of FIG. 18 through a software process, a programwhich realizes the following process is stored in the memory which isembedded in the image processor 100, and the CPU which reads the programperforms a process corresponding to the program.

In the image processor 100, the color correction target valuecalculation unit 112 totals the XYZ values of the image of the firstprojector PJ1 and the XYZ values of the image of the second projectorPJ2 for the respective gradations from black to white (Step S41). Thecolor correction target value calculation unit 112 applies the dimmingrates calculated in the light source luminance calculation unit 124 tothe projectors and then totals the XYZ values described above.

Next, the color correction target value calculation unit 112 calculatesthe XYZ target values in a stack state (Step S42), and ends a sequenceof processes (end). That is, the color correction value corresponds to avalue which is obtained by totaling the color characteristic values ofthe respective images in accordance with the dimming rates of the imageforming units. Since white should be corrected in a direction in whichbrightness is degraded, white matches the darkest color from among RGB.With regard to black, the average value of X, the average value of Y,and the average value of Z when display is performed with(R,G,B)=(0,0,0) and the dimming rates α and β are applied are useddirectly. With regard to an intermediate gradation, the color correctiontarget value calculation unit 112 performs correction as follows.

The color correction value which corresponds to the value obtained bytotaling the color characteristic values of the images, to which thedimming rates of the projectors (the image forming units) are applied,is used, and color correction is performed while a plurality of imageforming units are regarded as a single image forming unit. Accordingly,it should suffice that the color correction value common to the imageforming units is generated. For this reason, it is possible to achieveefficient color correction.

FIG. 19 is an operation explanatory view of the color correction targetvalue calculation unit 112. In FIG. 19, the horizontal axis representsinput data corresponding to a gradation and the vertical axis representsluminance.

For example, if the XYZ target values Dw of white and the XYZ targetvalues Dk of black in the stack state are set, the target value Yt of Yfrom among the XYZ target values of the intermediate gradation Di isobtained by the following expression. In the following expression, thecolor correction target value of white is Ywt, the color correctiontarget value of black is Ykt, and a gamma value is γ. Although inExpression (7), an example where the target value of Y is obtained isdescribed, X and Z are obtained in a similar manner.

Y _(t)=(Y _(wt) −Y _(kt))×((D _(i) −D _(k))/(D _(w) −D _(k)))^(γ) +Y_(kt)  (7)

As described above, in the first embodiment, the color correction targetvalue is set while the projectors in the stack state are regarded as asingle projector, and the color correction LUT shown in FIG. 17B isgenerated. The color correction LUT is the color correction LUT commonto the first projector PJ1 and the second projector PJ2, and the firstprojector PJ1 and the second projector PJ2 perform the same colorcorrection. The images are displayed in the stack state using the lightsources which are dimmed relative to the image signals subjected to thesame color correction in the projectors, thereby displaying the imageafter color correction shown in FIG. 17A.

According to the first embodiment, it is possible to improve the lightuse efficiency and to display a brighter image with the same powerconsumption while realizing image display with a target chromaticity.For example, when the first projector PJ1 has a characteristic shown inFIG. 9A and the second projector PJ2 has a characteristic shown in FIG.10A, it is assumed that power consumption or brightness duringprojection is simply in proportion to the amount of light of the lightsource. Specifically, when power consumption is 50% and just oneprojector is displayed, the luminance of the first projector PJ1 becomes132 cd/m², and the luminance of the second projector PJ2 becomes 101cd/m². At this time, when both projectors are in the stack state, theaverage luminance becomes 116 cd/m². Meanwhile, in the techniquedescribed in JP-A-2005-352171, the average luminance becomes 140 cd/m².According to the first embodiment, the average luminance becomes 158cd/m².

According to the first embodiment, since color correction is performedwhile a plurality of projectors are regarded as a single projector, itshould suffice that the color correction LUT is generated for oneprojector, thereby achieving efficient color correction.

First Modification of First Embodiment

In the first embodiment, with regard to target white of sRGB or thelike, a transformation matrix M which gives the relationship between RGBand XYZ becomes Expression (8-1), and for example, if the luminance isnormalized for white of sRGB, Expression (8-2) can be obtained.

$\begin{matrix}{\begin{bmatrix}X_{t} \\Y_{t} \\Z_{t}\end{bmatrix} = {{M\begin{bmatrix}R \\G \\B\end{bmatrix}} = {\begin{bmatrix}X_{R} & X_{G} & X_{B} \\Y_{R} & Y_{G} & Y_{B} \\Z_{R} & Z_{G} & Z_{B}\end{bmatrix}\begin{bmatrix}R \\G \\B\end{bmatrix}}}} & \left( {8\text{-}1} \right) \\{\begin{bmatrix}0.9505 \\1 \\1.089\end{bmatrix} = {\begin{bmatrix}0.4124 & 0.3576 & 0.1805 \\0.2126 & 0.7152 & 0.0722 \\0.0193 & 0.1192 & 0.9505\end{bmatrix}\begin{bmatrix}1 \\1 \\1\end{bmatrix}}} & \left( {8\text{-}2} \right)\end{matrix}$

If (Xt,Yt,Zt)=(0.9505,1,1.089) of Expression (8-2), the transformationmatrix M, the dimming rate α of the first projector PJ1, and the dimmingrate β of the second projector PJ2 are used, the XYZ values (Xp,Yp,Zp)after color correction and dimming are as follows.

$\begin{matrix}{\begin{bmatrix}R_{t} \\G_{t} \\B_{t}\end{bmatrix} = {\begin{bmatrix}{{\alpha \; X_{R}1} + {\beta \; X_{R}2}} & {{\alpha \; X_{G}1} + {\beta \; X_{G}2}} & {{\alpha \; X_{B}1} + {\beta \; X_{B}2}} \\{{\alpha \; Y_{R}1} + {\beta \; Y_{R}2}} & {{\alpha \; Y_{G}1} + {\beta \; Y_{G}2}} & {{\alpha \; Y_{B}1} + {\beta \; Y_{B}2}} \\{{\alpha \; Z_{R}1} + {\beta \; Z_{R}2}} & {{\alpha \; Z_{G}1} + {\beta \; Z_{G}2}} & {{\alpha \; Z_{B}1} + {\beta \; Z_{B}2}}\end{bmatrix}^{- 1}\begin{bmatrix}X_{t} \\Y_{t} \\Z_{t}\end{bmatrix}}} & \left( {9\text{-}1} \right) \\{R_{p} = {G_{p} = {B_{p} = {Y_{t} \times {\min \left( {{1\text{/}R_{t}},{1\text{/}G_{t}},{1\text{/}B_{t}}} \right)}}}}} & \left( {9\text{-}2} \right) \\{\begin{bmatrix}X_{p} \\Y_{p} \\Z_{p}\end{bmatrix} = {{M\begin{bmatrix}R_{p} \\G_{p} \\B_{p}\end{bmatrix}} = {\begin{bmatrix}0.4124 & 0.3576 & 0.1805 \\0.2126 & 0.7152 & 0.0722 \\0.0193 & 0.1192 & 0.9505\end{bmatrix}\begin{bmatrix}R_{p} \\G_{p} \\B_{p}\end{bmatrix}}}} & \left( {9\text{-}3} \right)\end{matrix}$

According to the first modification, with Expressions (9-1) to (9-3), insRGB, it is possible to improve the light use efficiency and to displaya brighter image with the same power consumption while realizing imagedisplay with a target chromaticity.

Second Modification of First Embodiment

Although in the first embodiment or the first modification, the optimumdimming rates α and β are obtained in each gradation, in a secondmodification, the dimming rates α and β which are obtained for white areused. In this case, while Yp does not conform to white luminance whichis obtained through color correction, it should suffice that therelative magnitude relationship when the combination of the dimmingrates α and β is changed is known. Accordingly, first, the optimumcombination of α and β is simply obtained using the set transformationmatrix M, the XYZ values (Xw1, Yw1, Zw1, Xw2, Yw2, Zw2) of white of thefirst projector PJ1 and the second projector PJ2 by Expressions (10-1)to (10-3). Only when detailed color correction is performed, accuratecolor correction is performed using Expressions (6-1) to (6-3) orExpressions (9-1) to (9-3). In this way, it is not necessary to obtainthe XYZ values of the RGB primary colors every time to construct atransformation matrix.

$\begin{matrix}\begin{matrix}{X_{w} = {{\alpha \; X_{w}1} + {\beta \; X_{w}2}}} \\{Y_{w} = {{\alpha \; Y_{w}1} + {\beta \; Y_{w}2}}} \\{Z_{w} = {{\alpha \; Z_{w}1} + {\beta \; Z_{w}2}}}\end{matrix} & \left( {10\text{-}1} \right) \\{\begin{bmatrix}R_{w} \\G_{w} \\B_{w}\end{bmatrix} = {{M^{- 1}\begin{bmatrix}X_{w} \\Y_{w} \\Z_{w}\end{bmatrix}} = {\begin{bmatrix}0.4124 & 0.3576 & 0.1805 \\0.2126 & 0.7152 & 0.0722 \\0.0193 & 0.1192 & 0.9505\end{bmatrix}^{- 1}\begin{bmatrix}X_{w} \\Y_{w} \\Z_{w}\end{bmatrix}}}} & \left( {10\text{-}2} \right) \\{R_{p} = {G_{p} = {B_{p} = {\min \left( {R_{w},G_{w},B_{w}} \right)}}}} & \left( {10\text{-}3} \right) \\{\begin{bmatrix}X_{p} \\Y_{p} \\Z_{p}\end{bmatrix} = {{M\begin{bmatrix}R_{p} \\G_{p} \\B_{p}\end{bmatrix}} = {\begin{bmatrix}0.4124 & 0.3576 & 0.1805 \\0.2126 & 0.7152 & 0.0722 \\0.0193 & 0.1192 & 0.9505\end{bmatrix}\begin{bmatrix}R_{p} \\G_{p} \\B_{p}\end{bmatrix}}}} & \left( {10\text{-}4} \right)\end{matrix}$

According to the second modification, it is possible to simplify thecalculation of the dimming rates α and β for optimum color correctionand dimming, to improve the light use efficiency, and to display abrighter image with the same power consumption while realizing imagedisplay with a target chromaticity.

Third Modification

Although in the first embodiment and the first modification or thesecond modification of the first embodiment, a configuration in whichthe image processor is externally attached to the two projectors eachhaving the image forming unit has been described, the invention is notlimited thereto. For example, the invention may be applied to an imagedisplay system which has a plurality of image forming units in ahousing, synthesizes image light from the image forming units in thehousing, and projects the synthesized image light on the screen SCR.

FIG. 20 is a block diagram showing a configuration example of an imagedisplay system according to a third modification of the firstembodiment. In FIG. 20, the same portions as those in FIG. 1 arerepresented by the same reference numerals, and description thereof willnot be repeated. With regard to the configuration of the first imageforming unit and the second image forming unit, a configuration whenviewed from the top is shown schematically.

A projector PJ includes a first image forming unit 164 a, a second imageforming unit 174 a, an image processing unit (image processor) 100 a, apolarization synthesis prism (Polarization Beam Splitter: PBS) 500, anda projection lens 510. The projector PJ projects two images formed bythe first image forming unit 164 a and the second image forming unit 174a in a superimposed manner, thereby displaying a stack image on thescreen SCR. The first image forming unit 164 a is different from thefirst image forming unit 164 in that no projection lens is provided, anda first unevenness correction LUT storage unit and a first unevennesscorrection process unit are provided. The second image forming unit 174a has the same configuration as the first image forming unit 164 a. Thatis, the second image forming unit 174 a is different from the secondimage forming unit 174 in that no projection lens is provided, and asecond unevenness correction LUT storage unit and a second unevennesscorrection process unit are provided. The image processing unit 100 ahas the same configuration as the image processor 100 in the firstembodiment or the first modification or the second modification of thefirst embodiment.

In the projector PJ, the first image forming unit 164 a modulates lightfrom the light source subjected to dimming control with the dimming rateα on the basis of an image signal after color correction for each colorcomponent of RGB, and synthesizes the color light components aftermodulation in a cross dichroic prism. Similarly, the second imageforming unit 174 a modulates light from a light source subjected todimming control with the dimming rate β on the basis of an image signalafter color correction for each color component of RGB, and synthesizesthe color light components after modulation in a cross dichroic prism.The polarization synthesis prism (synthesis unit) 500 synthesizes thesynthesized light from the first image forming unit 164 a and thesynthesized light from the second image forming unit 174 a, andirradiates the resultant light onto the projection lens 510. Theprojection lens 510 projects the light irradiated from the polarizationsynthesis prism 500 on a magnified scale to display an image on thescreen SCR.

The optical system of the first image forming unit 164 a and the opticalsystem of the second image forming unit 174 a are reversed. For thisreason, the image processing unit 100 a supplies, to the second imageforming unit 174 a, an image signal of the orientation of pixelshorizontally opposite to the orientation of pixels of an imagerepresented by an image signal supplied to the first image forming unit164 a. In this way, it is possible to arrange the direction of the imageformed by the first image forming unit 164 a and the direction of theimage formed by the second image forming unit 174 a.

In the third modification, the images formed by the first image formingunit 164 a and the second image forming unit 174 a accommodated in onehousing are projected on the screen SCR in a superimposed manner, suchthat a stack image is displayed. At this time, in the image processingunit 100 a, the same color correction and dimming control as in thefirst embodiment, the first modification, or the second modification areperformed, thereby obtaining the same effects as in the firstembodiment, the first modification, or the second modification.

Second Embodiment

Although in the first embodiment or the modifications of the firstembodiment, the optimization of color correction and dimming control hasbeen described, the invention is not limited thereto and may be appliedto the optimization of unevenness correction and dimming control. In asecond embodiment, color correction in the first embodiment or the firstmodification or the second modification of the first embodiment isperformed for respective points within the screen (a plurality of pixelpositions within the screen), thereby matching chromaticity over theentire screen and matching luminance between the points within thescreen.

FIG. 21 is a block diagram showing a configuration example of an imagedisplay system according to the second embodiment of the invention. InFIG. 21, the same portions as those in FIG. 1 are represented by thesame reference numerals, and description thereof will not be repeated.

An image display system 10 b of the second embodiment includes a firstprojector PJ1, a second projector PJ2, an image processor 100 b, animage signal supply device 200, and an operating unit 210. For theoptimization of unevenness correction and dimming, the image displaysystem 10 can include an unevenness measurement device 600 and a sensor400.

The image processor 100 b generates an unevenness correction value foran unevenness correction process corresponding to each projector on aninput image signal in accordance with a designated dimming rate, andcontrols the dimming of at least one of the first projector PJ1 and thesecond projector PJ2. The image processor 100 b has the sameconfiguration as in FIG. 2, and includes an unevenness correction valuecalculation unit, instead of the color correction value calculation unit110 of FIG. 2. The unevenness correction value calculation unit includesan unevenness correction target value calculation unit and an unevennesscorrection LUT generation unit.

The unevenness measurement device 600 is a two-dimensional image sensor,such as a CCD (Charge Coupled Device) sensor, and is provided to measurean image projected on the screen SCR. The unevenness measurement device600 captures a gray image and a solid image including an intermediategradation of 0% to 100% of RGB displayed on the screen SCR by theprojectors during unevenness measurement. The unevenness measurementdevice 600 acquires XYZ tristimulus values of the CIE 1931 colorimetricsystem or RGB in-plane distribution (intensity distribution) informationas color characteristic values. As the unevenness measurement device600, one (for example, ProMetric manufactured by Radiant Imaging, or thelike) which captures an image using a filter with spectral sensitivityapproximate to an xyz color-matching function, and obtains XYZtristimulus values through a matrix correction operation is used. As theunevenness measurement device 600, one which captures an image using aRGB filter different from a color-matching function to obtain a RGBimage may be used. The in-plane distribution information acquired by theunevenness measurement device 600 for each projector is sent to theimage processor 100 b as the color characteristic values (intensitydistribution of luminance/chromaticity) which are the unevennessmeasurement values. The measurement process in the unevennessmeasurement device 600 may be performed under the control of the imageprocessor 100 b.

FIG. 22 is a flowchart of an example of an image process in the imagedisplay system 10 b of the second embodiment. Although the image processshown in FIG. 22 is performed in the image processor 100 b, the firstprojector PJ1, and the second projector PJ2, the overall process may beperformed in the image processor 100 b.

First, the image processor 100 b receives operation information from theoperating unit 210 or sensor information from the sensor 400 to receivea designated dimming rate (Step S100 b). The image processor 100 b mayperform a process for determining the designated dimming rate on thebasis of the operation information from the operating unit 210 or thesensor information from the sensor 400.

Next, the dimming control unit 140 references the dimming rate storageunit 130 and controls the dimming of the image forming units with thedimming rates set in the image forming units in response to thedesignated dimming rate received in Step S100 b (Step S102 b, a dimmingcontrol step).

Each projector includes an unevenness correction LUT storage unit. Eachprojector performs an unevenness correction process on an image signalcorresponding to the image forming unit using the unevenness correctionvalue corresponding to the dimming rate of the corresponding imageforming unit in Step S102 b (Step S104 b, an unevenness correctionprocess step). Step S102 b and S104 b may be reversed. In eachprojector, the image signal subjected to the unevenness correctionprocess in Step S104 b is supplied to the corresponding image formingunit (Step S106 b), and a sequence of processes ends (end).

Accordingly, through the cooperation with the unevenness correctionprocess which realizes display of a stack image with a uniform targetchromaticity without unevenness, it is possible to adjust the luminanceof the light sources of the projectors with the dimming rates differentfrom the designated dimming rate. As a result, it is possible toincrease the light use efficiency without wastefully decreasing theluminance of the light source.

FIG. 23 is a flowchart of a process example of the image processor 100b.

FIG. 24 is a flowchart of an example of an unevenness measurementprocess in Step Sib of FIG. 23.

When the image processor 100 b realizes the process of FIG. 23 or 24through a software process, a program which realizes the followingprocess is stored in the memory which is embedded in the image processor100 b, and the CPU which reads the program performs a processcorresponding to the program.

First, the image processor 100 b controls the unevenness measurementdevice 600 and acquires an XYZ value distribution, which is themeasurement result of the unevenness measurement device 600, as theunevenness measurement values of the projectors (Step Sib).

In Step S1 b, first, each projector projects one of the solid images ofthe entire screen of the respective gradations of gray and RGB colors onthe screen SCR (Step S11 b). In this state, the image processor 100 bperforms control for measuring the XYZ value distribution within thescreen using the unevenness measurement device 600, and acquires the XYZvalues as the unevenness measurement values (Step S12 b) Thereafter,when the entire measurement does not end (Step S13 b: N), the imageprocessor 100 b returns to Step S11 b, and projects the next solid imageon the screen SCR. In this way, if the unevenness measurement values areacquired for all the solid images of the entire screen of the respectivegradations of gray and RGB colors (Step S13 b: Y), the image processor100 b ends the process of Step S1 b (end).

Subsequently, the image processor 100 b obtains target light sourceluminance from the operation information from the operating unit 210 orthe sensor information from the sensor 400 in the designated dimmingrate generation unit 122, and sets a designated dimming rate δcorresponds to the target light source luminance (Step S2 b).

The image processor 100 b calculates the light source luminance of theprojectors from the XYZ value distribution of white and the target lightsource luminance (=designated dimming rate δ) in the light sourceluminance calculation unit 124, and obtains the dimming rates α and βcorresponding to the light source luminance (Step S3 b).

Next, the image processor 100 b calculates the unevenness correctiontarget value in the stack state in each gradation from the light sourceluminance of the projectors and the unevenness measurement values in therespective gradations of the projectors acquired in Step Sib in theunevenness correction target value calculation unit (not shown) (Step S4b).

Thereafter, the image processor 100 b generates the unevennesscorrection LUT on the basis of the unevenness correction target value inthe unevenness correction LUT generation unit (not shown) (Step S5 b).

The unevenness correction LUT generated in Step S5 b is stored in theunevenness correction LUT storage unit of each projector. Subsequently,the image processor 100 b performs dimming control of the projectorswith the dimming rates calculated in Step S3 b, and performs theunevenness correction process with reference to the unevennesscorrection LUT generated in Step S5 b.

FIG. 25 is a flowchart of an example of a light source luminancecalculation process in Step S3 b of FIG. 23.

First, prior to searching the dimming rates α and β, the light sourceluminance calculation unit 124 performs the initial settings of thedimming rates α and β corresponding to the light source luminance andthe luminance Yp after dimming (Step S31 b).

Next, the light source luminance calculation unit 124 calculatesluminance Yq after dimming (Step S32 b).

In Step S32 b, first, the light source luminance calculation unit 124performs the initial setting of the in-plane minimum value of theluminance Yq after dimming (Step S321 b). Next, the light sourceluminance calculation unit 124 obtains the value of the right side ofExpression (6-3) using the dimming rates α and β and sets the value to avariable Yr (Step S322 b). Subsequently, the light source luminancecalculation unit 124 compares Yq with Yr obtained in Step S322 b (StepS323 b), and when Yq is greater than Yr (Step S323 b: Y), substitutes Yrinto Yq as the in-plane minimum value of the luminance after dimming(Step S324). When Yq is equal to or smaller than Yr, Yq is maintained.When all the in-plane positions are not completed (Step S325 b: N), thein-plane position is updated (Step S326 b), and the process returns toStep S322 b.

When all the in-plane positions are completed (Step S325 b: Y), thelight source luminance calculation unit 124 compares Yp with Yq at thattime (Step S33 b). When Yq is greater than Yp (Step S33 b: Y), the lightsource luminance calculation unit 124 updates the dimming rates α and βcorresponding to Yq as an optimum light source luminance, andsubstitutes Yq into the luminance Yp after dimming (Step S34 b).

When all the combinations of the light source luminance do not end (StepS35 b: N), the light source luminance calculation unit 124 updates thedimming rates α and β (Step S36 b), and the process returns to Step S321b.

In Step S35 b, when all the combinations of the light source luminanceend (Step S35 b: Y), the light source luminance calculation unit 124ends a sequence of processes (end), and determines the dimming rates αand β at that time as the dimming rates of the projectors.

FIG. 26 is an explanatory view of an example of a light source luminancecalculation process according to the second embodiment. FIG. 26 shows anexample of a process for calculating the dimming rates α and 13, inwhich the minimum value of Y from among the XYZ values within the planeis maximal, at nine points (pixel positions P1 to P9) within the screen.

FIG. 27 shows a calculation example of the dimming rates α and β usingthe light source luminance calculation unit according to the secondembodiment. FIG. 27 shows the relationship between the dimming rate αand in-plane minimum luminance when the color characteristic of thefirst projector PJ1 is as shown in FIG. 9A and the color characteristicof the second projector PJ2 is as shown in FIG. 10A. In FIG. 27, thehorizontal axis represents α and the vertical axis represents luminance.

As a result of applying the combination of the dimming rates α and β tothe XYZ values of white of the first projector PJ1 and the secondprojector PJ2 at each position within the screen, as shown in FIG. 26,the pixel position P4 when the dimming rate α is 0.5 has the in-planeminimum luminance. Meanwhile, the pixel position P2 when the dimmingrate α is 0.65 has the in-plane minimum luminance. As described above,if the in-plane minimum luminance changes as shown in FIG. 27 whilechanging the dimming rate α(β), it is understood that, when the dimmingrate α is 0.65 and the dimming rate β is 0.35, the in-plane minimumluminance has a maximum value.

If the dimming rates α and β are obtained in the above-described manner,as in the first embodiment, in Steps S4 b and S5 b of FIG. 23, theunevenness correction target value in the stack state is calculated.That is, it should suffice that the XYZ values in the stack state of therespective gradations from black to white are obtained at each in-planeposition, and the color correction LUT at each in-plane position isgenerated as an unevenness correction LUT.

Although in the second embodiment, a configuration in which the imageprocessor is externally attached to the two projectors each having theimage forming unit has been described, the invention is not limitedthereto. For example, as in the third modification of the firstembodiment, the second embodiment may be applied to an image displaysystem which has a plurality of image forming units in a housing,synthesizes image light from the image forming units in the housing, andprojects the synthesized image light on the screen SCR.

As described above, according to the second embodiment, it is possibleto improve the light use efficiency and to display a brighter image withthe same power consumption while realizing image display with a uniformtarget chromaticity without unevenness. At this time, since colorcorrection is performed while a plurality of projectors are regarded asa single projector, it should suffice that the unevenness correction LUTis generated for one projector, thereby achieving efficient unevennesscorrection.

Although the image processing method, the projector, the image displaysystem, and the like according to the invention have been described onthe basis of the foregoing embodiments or the modifications, theinvention is not limited to the foregoing embodiments or themodifications. Various modifications may be made without departing fromthe subject matter of the invention. For example, the followingmodifications may be made.

(1) Although in the foregoing embodiments or the modifications, anexample where images formed by two image forming units are stacked hasbeen described, the same applies to a case where images formed by threeor more image forming units are stacked. In this case, since thecombinations of the light source luminance of the image forming unitsbecome enormous, it is desirable to increase the dimming rate changestep or to place a restriction on the minimum value of the dimming rateof each projector.

(2) Although in the foregoing embodiments or the modifications, lightreduction when dimming is performed has been described, the invention isnot limited thereto. For example, the improvement in brightness withlight increasing can be realized through the same process. It shouldsuffice that the designated dimming rate δ is δ≧1.

(3) Although in the foregoing embodiments or the modifications, theprojector has been described, the invention is not limited thereto. Theinvention can be of course applied to all apparatuses which displayimages on the basis of image signals in a superimposed manner.

(4) Although in the foregoing embodiments or the modifications, anexample where an image forming unit is an optical modulator using aso-called three-plate transmissive liquid crystal panel has beendescribed, an optical modulator using a single-plate, two-plate, or fouror more-plate transmissive liquid crystal panel may be used. Although acase where a light valve using a transmissive liquid crystal panel isused as an optical modulator has been described, the invention is notlimited thereto. For example, a DLP (Digital Light Processing)(Registered Trademark), an LCOS (Liquid Crystal On Silicon), or the likemay be used as an optical modulator.

(5) Although in the foregoing embodiments or the modifications, theinvention has been described as an image processing method, an imageprocessor, an image display system, and the like, the invention is notlimited thereto. For example, the invention may relate to a program inwhich the procedure of an image processing method according to theinvention, a method of generating a color correction value, or a methodof generating an unevenness correction value is described, a program inwhich the procedure of a processing method (image display method) of animage display device for realizing the invention is described, or arecording medium having recorded thereon any of these programs.

The entire disclosure of Japanese Patent Application No. 2011-152739,filed Jul. 11, 2011 is expressly incorporated by reference herein.

What is claimed is:
 1. An image processing method which performs colorcorrection on a superimposed image obtained by superimposing a firstimage formed by a first image forming unit and a second image formed bya second image forming unit, the method comprising: controlling thedimming of the first image forming unit and the second image formingunit on the basis of dimming rates set in the first image forming unitand the second image forming unit in response to a given designateddimming rate.
 2. The method according to claim 1, further comprising:calculating a color correction target value corresponding to the firstimage forming unit and the second image forming unit on the basis of avalue obtaining by totaling color characteristic values of the firstimage and the second image in accordance with the dimming rates of thefirst image forming unit and the second image forming unit; andgenerating the color correction value corresponding to the first imageforming unit and the second image forming unit on the basis of the colorcorrection target value calculated in the calculating of the colorcorrection target value, wherein, in the performing of the colorcorrection process, the color correction process is performed using thecolor correction value generated in the generating of the colorcorrection value.
 3. The method according to claim 1, furthercomprising: calculating the dimming rates of the first image formingunit and the second image forming unit on the basis of the designateddimming rate and color characteristic values of the first image and thesecond image, wherein, in the controlling of the dimming, the dimming ofthe first image forming unit and the second image forming unit isperformed on the basis of the dimming rates calculated in thecalculating of the dimming rates.
 4. The method according to claim 1,wherein the average value of the dimming rates of the first imageforming unit and the second image forming unit is equal to thedesignated dimming rate.
 5. An image processor which performs colorcorrection on a superimposed image obtained by superimposing a firstimage formed by a first image forming unit and a second image, formed bya second image forming unit, the image processor comprising: a dimmingcontrol unit that controls the dimming of the first image forming unitand the second image forming unit on the basis of dimming rates set inthe first image forming unit and the second image forming unit inresponse to a given designated dimming rate.
 6. The image processoraccording to claim 5, further comprising: a light source luminancecalculation unit that calculates the dimming rates of the first imageforming unit and the second image forming unit on the basis of thedesignated dimming rate and the color characteristic values of the firstimage and the second image, wherein the dimming control unit controlsthe dimming of the first image forming unit and the second image formingunit on the basis of the dimming rates calculated by the light sourceluminance calculation unit.
 7. An image display system comprising: theimage processor according to claim 5; a first image display device thathas the first image forming unit whose dimming is controlled by thedimming control unit; and a second image display device that has thesecond image forming unit whose dimming is controlled by the dimmingcontrol unit.
 8. An image display system comprising: the image processoraccording to claim 6; a first image display device that has the firstimage forming unit whose dimming is controlled by the dimming controlunit; and a second image display device that has the second imageforming unit whose dimming is controlled by the dimming control unit.